Of all the impacts of , extreme heat is one of the least visible – until, in retrospect, between sweltering temperatures and . A new study of 53 million births over 25 years across the US has now found that early births become slightly more frequent during hotter, longer heatwaves. Similar to the elderly, pregnant people, newborns, and infants are particularly sensitive to the effects of extreme heat, as easily as the rest of us.
University of Nevada epidemiologist Lyndsey Darrow and colleagues analyzed national birth records between 1993 and 2017 across the 50 most populous metropolitan areas of the United States, a country where heatwaves have become 24 percent more intense and are occurring . Excluding rural areas not captured in the data, the researchers found that daily rates of preterm birth (between 28 and less than 37 weeks' gestation) and early-term birth (37 to less than 39 weeks) increased a small amount as local temperatures rose, particularly among lower socioeconomic groups. Because an observational study like this can't elucidate direct causes, those are only associations, but they became stronger as temperatures increased and heatwaves stretched on, between four and seven days.
Regardless of whether heatwaves were defined using average temperatures, overnight minimums or daily maximums, the same effect was found. Previous research on extreme heat has linked prolonged heatwaves with rises in , , and deaths. Almost from heat-related causes during the European .
